1. Field of the Invention
The present invention generally relates to a heat exchanger, such as a condenser or an evaporator, and more particularly, to heat exchangers including at least one tank unit through which the heat medium is conducted through a plurality of pipe members.
2. Description of the Prior Art
A heat exchanger, such as an evaporator for use in an automotive air conditioning systems, as illustrating in FIG. 1, is well known in the art. For example, such heat exchangers are described in U.S. patent application Ser. No. 08/352,808, which is hereby incorporated by reference.
Referring to FIG. 1, an evaporator 100 includes an upper tank 110 and a lower tank 120 which is vertically spaced from upper tank 110. Upper and lower tanks 110 and 120 may be made of an aluminum alloy and are rectangular parallelepiped in shape. Evaporator 100 further includes a plurality of heat exchange units 130 at which an exchange of heat occurs. Each of heat exchange units 130 also may be made of an aluminum alloy and includes a plurality identical circular pipe portions 131 which are spaced from one another at about equal intervals and a plurality of plane portions 132 which extend between adjacent pipe portions 131. In each heat exchange unit 130, pipe portions 131 and plane portions 132 are arranged such that the longitudinal central axes of pipe portions 131 are located in the same plane as plane portions 132.
Heat exchange units 130 may be arranged in parallel in a direction of length of evaporator 100, indicated by axis Y.sub.1 -Y.sub.2 of the three-dimensional coordinates shown in FIG. 1, at substantially equal intervals, and may extend between upper and lower tanks 110 and 120. Upper and lower tanks 110 and 120 are placed in fluid communication through pipe portions 131 of heat exchange units 130. As illustrated in FIG. 2, pipe portions 131 of adjacent heat exchange units 130 are offset by one half of the length of the interval between adjacent pipe portions 131. Furthermore, directions of width and height of evaporator 100 are indicated by axis X.sub.1 -X.sub.2 and axis Z.sub.1 -Z.sub.2 of the three-dimensional coordinates shown in FIG. 1, respectively. Moreover, axes X.sub.1 -X.sub.2 and Y.sub.1 -Y.sub.2 in FIG. 2, axes Y.sub.1 -Y.sub.2 and Z.sub.1 -Z.sub.2 in FIG. 4, and axes X.sub.1 -X.sub.2 and Z.sub.1 -Z.sub.2 in FIG. 5 correspond to the axes of the three-dimensional coordinates shown in FIG. 1.
Referring to FIGS. 3-5, evaporator 100 is provided with a plurality of louvers 133 formed in plane portions 132. Each louver 133 is parallel to a plane which is perpendicular to the longitudinal central axes of pipe portions 131. As a result of forming louvers 133, generally hexagonal openings 135 are formed in plane portions 132 at the positions which are located between the adjacent louvers 133. Although only some of the louvers 133 are illustrated in FIG. 1, louvers 133 are formed in each plane portion 132 and are arranged from the upper to lower ends of each plane portion 132.
Referring to FIG. 1 again, an interior space of the upper tank 110 is divided by partition plate 140 into a first chamber section 111 and a second chamber section 112. Upper tank 110 is provided with an inlet pipe 150 fixedly connected through an outside end surface of first chamber section 111 and an outlet pipe 160 fixedly connected through an outside end surface of second chamber section 112. Furthermore, when evaporator 100 is installed, heat exchange units 130 are oriented so that plane portions 132 are aligned perpendicular to the flow direction of air "A" which passes through evaporator 100. Consequently, pipe portions 131 also are perpendicular to the flow direction of the air passing through evaporator 100. The flow direction of the air passing through evaporator 100 also is indicated by arrow "A" in FIGS. 2, 3, and 5.
During operation of the automotive air conditioning system, the refrigerant fluid is conducted into first chamber section 111 of upper tank 110 from an element of the automotive air conditioning system, such as a condenser (not shown), via inlet pipe 150. The refrigerant fluid in first chamber section 111 flows downwardly through a first group of pipe portions 131 of heat exchange units 130. In doing so, the refrigerant fluid absorbs heat from the air flowing across the exterior surfaces of heat exchange units 130 through plane portions 132 and pipe portions 131.
The refrigerant fluid then flows into a first portion of an interior space of lower tank 120, which corresponds to first chamber section 111. Thereafter, the refrigerant fluid flows to a second portion of the interior space of lower tank 120, which corresponds to second chamber section 112, and then flows upwardly through a second group of pipe portions 131 of heat exchange units 130. In doing so, the refrigerant fluid further absorbs heat from the air flowing across the exterior surfaces of heat exchange units 130 through plane portions 132 and pipe portions 131.
Then, the refrigerant fluid flows into second chamber section 112 of upper tank 110. The refrigerant fluid in second chamber section 112 then is conducted to other elements of the automotive air conditioning system, such as a compressor (not shown), via outlet pipe 160.
Referring to FIGS. 1-3, the heat exchange operation in this prior art evaporator 100 is further described below. When the air passes through evaporator 100, two air flow paths, which are indicated by arrows "B" and "C" (FIG. 2), respectively, are generally generated. In the air flow path indicated by arrows "B", the air passes through openings 135 in a direction indicated by axis X.sub.1 -X.sub.2 along louvers 133. On the other hand, in the air flow path indicated by arrows "C'", the air flows along an exterior surface of an upstream semicylindrical region of circular pipe portions 131 until it collides with the surface which is located at the boundary between pipe portions 131 and plane portions 132. Thereafter, the air flows into opening 135. In both air flow paths indicated by arrows "B" and "C'", the heat from the air is absorbed through plane portions 132 and/or pipe portions 131 and transferred to the refrigerant fluid.
Since the path of the air which passes through evaporator 100 is narrowed between the adjacent pipe portions 131, the speed of the air flow increases. As a result, the speed of the air flow is maximized at plane portions 131, of each heat exchange unit 130. Since the air collides with the surface between pipe portions 131 and plane portions 132 with the maximum flow speed, the flow resistance caused thereby becomes large. The flow resistance of the air passing through evaporator 100 sometimes increases to an extent that evaporator 100 performs inefficiently.
Furthermore, in the air flow path indicated by arrows "C'", the air flowing along the exterior surface of the upstream semicylindrical region of the circular pipe portions 131 changes its flow direction at the boundary between pipe portions 131 and plane portions 132. As a result, only a small portion of the air which has passed through the opening 135 flows along the exterior surface of the downstream semicylindrical region of circular pipe portions 131. Therefore, the heat exchange between the air and the downstream semicylindrical region of circular pipe portions 131 is insignificant, causing inefficient heat exchange at each heat exchange unit 130.